increase default revocation_cache_time
increase default revocation_cache_time

1 second was originally intended as a useful value for testing purposes,
but was never intended to be a production-friendly default. Raising the
default value to match the default token_cache_time results in better
production performance.

Change-Id: I03939d41bc50b32a6aa5ebf93eb71103e16e988f
Related-Bug: 1287301

varunarya10/keystonemiddleware